Synaptogenesis is regulated by both activity-dependent and independent mechanisms. Activity-dependent regulation of synaptogenesis is mediated, in part, by changes in gene expression. Therefore an important goal of neuroscientists is to understand the mechanisms by which synaptic activity is transduced to the genome to influence synapse formation. The neuromuscular junction (NMJ) is a well studied model for identifying and characterizing the mechanisms by which synaptic activity influences synapse formation and regulates gene expression. Although activity-dependent control of NMJ formation has been studied for decades, the underlying molecular mechanisms are poorly understood. We recently identified a Dach2-dependent signal transduction cascade that contributes to activity-dependent expression of nAChR and MuSK genes. Therefore, this signaling cascade along with the previously reported HDAC9 (MITR) signaling cascade, that also participates in activity-dependent nAChR gene expression, represent good candidates for mediating the effects of synaptic transmission on NMJ formation. In this grant application we propose to use a combination of genetic approaches and cell and molecular biological approaches to investigate the role Dach and MITR signaling play in regulating NMJ formation and controlling gene expression by nerve-induced muscle depolarization. Knockout animals will be used to study NMJ development, while innervated and denervated skeletal muscle will be used to study nerve-induced, activity-dependent gene regulation. Specifically, we propose to: 1) Evaluate the role Dach2 and MITR play during development of the NMJ; 2) Examine if HDAC4 coordinates Dach2 and MITR gene repression in response to muscle innervation; and 3) Determine if the Dach interacting proteins Six and Eya participate in activity-dependent regulation of gene expression. This research will identify mechanisms by which muscle activity regulates synapse formation during development and modifies synapse and muscle function in the adult. Although this research is of a basic nature, it may suggest ways of enhancing synapse formation, synaptic plasticity and muscle function in the injured, diseased or aged individual. PUBLIC HEALTH RELEVANCE: The studies in this grant application aim to understand how muscle activity signals to the genome to regulate neuromuscular development, muscle atrophy and muscle gene expression. These studies will not only further our understanding of the mechanisms underlying these events, but may also suggest novel strategies for restoring neuromuscular communication and improving muscle function following injury or disease.